1. Field of the Invention
The present invention relates to cermets used for tools such as coating tools, spike pins, scrapers, hobs, reamers, screw drivers, and so forth.
2. Prior Art
Conventionally, TiC (the chemical formula for carbon titanium; hereinafter, chemical formula or chemical symbols are used to denote chemical elements and compounds) base and Ti(C, N) base cermets have been paid attention because a) raw materials for the types of cermets are less expensive, b) the types of cermets have stronger oxidation-resistance so that tools made of such materials are less subject to oxidation during high-speed cutting in which the tools are exposed to high temperature, c) such cermets offer stronger adhesion-resistance in high temperature, and d) such cermets are chemically more stable. So the tools made of these materials are less liable to wear which occurs due to their affinity to the material to be cut when WC base alloys (cemented carbide).
This type of cermet, however, has a limited scope of application because 1) its mechanical breaking-resistance (referred to as breaking-resistance hereinafter), 2) crack extension-resistance due to thermal shock or uneven distribution of heat (referred to as thermal shock-resistance hereinafter), and 3) plastic deformation-resistance in high temperature or under high pressure (referred to as plastic deformation-resistance hereinafter) are not quite satisfactory.
Lately, sintered bodies having a hard dispersed phase (carbonitride phase) made of carbide, nitride, and carbonitride of transitional metals in groups IVb, Vb, and VIb have been proposed to overcome the problems described above. Further, various propositions have been made on the structure and composition of such sintered bodies with the aim of improving the properties of cermet (see Japan Published Examined Patent Application No. S 63-3017).
For instance, a proposed cermet containing N has WC and carbide, nitride, and carbonitride of transitional metals in group Vb. Structurally, such a cermet contains a hard dispersed phase comprising TiN single phase particles (single structural particles) and dual phase particles in which the cores are rich in transitional metals in groups IVb and the outer layers are rich in transitional metals in group Vb and VIb.
However, a sintered body having such a hard dispersed phase as described above has not successfully enhanced such performance characteristics as breaking-resistance, thermal shock-resistance, and plastic deformation-resistance without impairing the cermet's inherent properties.
More particularly, if substances such as WC and carbide, nitride, and carbonitride of transitional metals in group Vb are added to a cermet to improve breaking-resistance, thermal shock-resistance, and plastic deformation-resistance, dual phase particles grow in number, which reduces mechanical wear-resistance (referred to as wear-resistance hereinafter), and adhesion-resistance in a high temperature (referred to as temperature adhesion-resistance hereinafter).